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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 18th Mar 2019, 15:39
  #1941 (permalink)  
 
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Originally Posted by FCeng84 View Post
Don't forget that slowing to about 250 knots also allows the control system to use full elevator travel. At speeds above that "blowdown" or "blowback" (choose your desired label) occurs and the system is not able to push the elevator to its full travel limits.
Bingo, you are reducing the effectiveness of the miss trimmed stab and increasing elevator effectiveness.
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Old 18th Mar 2019, 16:22
  #1942 (permalink)  
 
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Apologies if already posted

Sensor cited as potential factor in Boeing crashes draws scrutiny

March 17 at 7:47 PM

https://www.washingtonpost.com/busin...=.b9df74af9cb0


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Old 18th Mar 2019, 16:35
  #1943 (permalink)  
 
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Sounds like they were stuck between a rock and a hard place

Reduce thrust - immediate reaction is a slight reduction in pitch due to thrust coupling but maybe they would slow down and recover enough elevator authority to begin a stable climb eventually
vs.
Maintain / increase thrust - maybe a slight pitch increase to start with but they will gain speed with limited elevator travel and no chance of overcoming the nose down moment from the stab

Option 1 probably works nicely at when you have altitude on your side...
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Old 18th Mar 2019, 16:52
  #1944 (permalink)  
 
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Question for all the pros: if MCAS is supposed to AVOID stalls by putting the nose down, does anyone know how many times it actually DID this on all airlines since it was introduced? Is there some sort of log of when it was activated, and is there any analyses of valid/invalid activation? Or, is this asking too much? Seems to me this would be extremely relevant history.
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Old 18th Mar 2019, 16:53
  #1945 (permalink)  
 
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"Prosecutors, Transportation Department Scrutinize Development of Boeing’s 737 MAX"

https://www.wsj.com/articles/faas-73...d=hp_lead_pos1
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Old 18th Mar 2019, 17:11
  #1946 (permalink)  
 
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Originally Posted by Running Ridges View Post
Sounds like they were stuck between a rock and a hard place

Reduce thrust - immediate reaction is a slight reduction in pitch due to thrust coupling but maybe they would slow down and recover enough elevator authority to begin a stable climb eventually
vs.
Maintain / increase thrust - maybe a slight pitch increase to start with but they will gain speed with limited elevator travel and no chance of overcoming the nose down moment from the stab

Option 1 probably works nicely at when you have altitude on your side...
They had a much easier choice, comply with the QRH for runaway trim, disconnect the trim system, manually trim and fly to destination as airline crews have been doing since the invention of electric trim.
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Old 18th Mar 2019, 17:13
  #1947 (permalink)  
 
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Automation has been taking over cockpits for decades. Flight engineers have all but disappeared and the second officers filling their seats are gone too, along with the high time, well seasoned first officers who were often more experienced than their captains due to mergers and takeovers. These days, it must feel pretty lonely up there on a bad night with a copilot new to the airplane and the game. Automation, now so essential but not always cooperative or fully understood, only adds to the percentage of recent accidents due to confusion over who or what had control of the airplane.The writing is clearly on the wall. According to at least one source, Boeing believes eighty five percent of all accidents are due to pilot error, and there are those who think the sooner the day comes when the AI does the all work and the pilot does all the cross checking, the better.

The flying public are unlikely to accept security guards and night watchmen minding the machinery however, so real pilots will be with us for the foreseeable future.. Despite the shift in perception, away from the status and prestige of airline pilots in previous generations, they need to be a lot smarter in ways we old stick and rudder guys would never have dreamed of. Know your airplane is as important now as it ever was, but training is apparently too expensive and the task is not made any easier when the builders don’t think the pilots are up to it. Until they can design airplanes with pilots completely out of the loop, they need to be completely within it. Right up until the last one out of the cockpit turns out the lights.
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Old 18th Mar 2019, 17:14
  #1948 (permalink)  
 
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Originally Posted by Sailvi767 View Post


They had a much easier choice, comply with the QRH for runaway trim, disconnect the trim system, manually trim and fly to destination as airline crews have been doing since the invention of electric trim.
Yes, we know...
The billion $ question is: Why went two crews into that deadly trap?
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Old 18th Mar 2019, 17:24
  #1949 (permalink)  
 
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Originally Posted by Sailvi767 View Post
They had a much easier choice, comply with the QRH for runaway trim . . .
Except that MCAS activation doesn't present as runaway trim (not continuous and can be briefly interrupted by operation of column trim switches), so it wasn't recognized by at least two crews. Then there's the problem of trimming manually, perhaps from full nose-down, at high speed and low altitude, while trying to fly the airplane -- with any number of other distractions bombarding the senses and causing distraction and confusion.

This has been discussed exhaustively and compellingly in these threads, but some still insist that the problem is pilot error. I suppose it's OK for individual pilots to think that way, but, when engineers, manufacturers, regulatory authorities, etc. do, the result is all too likely to be catastrophic loss.



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Old 18th Mar 2019, 17:53
  #1950 (permalink)  
 
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Devil

Originally Posted by FGD135 View Post
Quite commonplace, really, for critical airborne systems to use only one sensor, and only raw data at that. Examples:

Turkish Airlines flight 1951, 25 Feb, 2009. B737-800 where one radar altimeter was malfunctioning. The data from the sensor went to zero, the computers thought the plane was on the ground, so they reduced the engine power to idle. The result was a stall at low altitude where many occupants were killed. The idiotic thing was that not only were the computers using just one radar altimeter sensor, they were making no effort to inspect it for reasonableness or filter it against spikes. The data was showing valid heights but then instantly started showing zeros!

Qantas flight 72, 7 Oct, 2008. Airbus A330. Pilot's side air data computer had a momentary spike in the angle of attack data. Silly computers took this as indicating the aircraft was suddenly stalling, and at a speed of about 450 knots, pushed the nose down. Passengers were thrown into the ceiling and many were seriously injured. The idiotic thing was that the computers were using completely raw data and could therefore believe that the angle of attack could, in the space of one second, change from sensible values to a stalling angle. Also idiotic that the computers would happily perform a manouever of such violence.
Well I've only been an aviation professional for 52 years, so what do I know. Seriously though, the Turkish Airlines case illustrated poor failure monitoring within the RADALT (Not to MENTION complete crew unawareness and monitoring) of IAS. RAD ALT inputs to AFCS typically is used for gain gearing and throttle retard and usually have good self monitoring (But not in this case of course).
The QANTAS A330 case has yet to be completely and adequately explained ADIRU fault, the suspect was a data labelling issue. (GREAT airmanship by the QANTAS crew however). The ADIRU functions certainly are monitored and compared.
For ANY flight control system, ALPHA as well as Ps & Pt inputs are invariably monitored.. The absence of an Alpha disagree function of MCAS is at the very best negligent to the extreme, as has been the whole frantically rushed throwing together of this appalling system. Pilots and passengers deserve FAR better than this.
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Old 18th Mar 2019, 18:06
  #1951 (permalink)  
 
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How many times does it have to do the same thing before you consider it to be continuously doing something you do not want. My number would be 2.
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Old 18th Mar 2019, 18:11
  #1952 (permalink)  
 
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The Seattle Times runs an article with some bold claims, including that factual errors have crept in the certification process, and where raised to the attention of Boeing and FAA days before the ET302 crash. It is not paywalled where I stand.
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Old 18th Mar 2019, 18:16
  #1953 (permalink)  
 
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Originally Posted by flyingchanges View Post
It is runaway stab trim...
Maybe not all at once, but if it is not doing what you want, then it is out of control.
Clearly MCAS is not a runnaway trim condition, otherwise we would be reaching for the cut-out switches every time the speed-trim operated. I think some people here do not realise that the trimmer doing its own thing is operations normal.

And the auro-trim systems are always mis-trimming the aircraft (the trim inputs by the speed-trim system are always wrong, and you always have to re-trim manually). So at what point does ‘operations normal’ become ‘operations abnormal’? At what point do you assume that the trimmer has gone awry..??

Silver
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Old 18th Mar 2019, 18:33
  #1954 (permalink)  
 
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Originally Posted by DaveReidUK View Post
Interesting graphic.

The altitude spike where the aircraft dips below the runway surface(!) accompanied by a single, instantaneous 2000+ fpm ROC value is clearly an artifact (unless Newton got it all wrong), probably coinciding with rotation.

There is a similar, spurious altitude spike towards the RH edge of the plot, which you have wisely ignored - that one is easier to account for because a distance-vs-time plot shows the aircraft flying backwards at that point (i.e. it's a timestamp anomaly rather than bad ADS-B data).
In addition to often mentioned lack of fidelity in the ads-b info available on the internet. It is normal to see a VSI indication dip slightly at rotation. well, it used to be, not familiar with the most recent 15 years of aircraft development.
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Old 18th Mar 2019, 18:37
  #1955 (permalink)  
 
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Any reason there is not a warning light on the 737 MAX to indicate MCAS has activated?
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Old 18th Mar 2019, 18:38
  #1956 (permalink)  
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Originally Posted by flyingchanges View Post
How many times does it have to do the same thing before you consider it to be continuously doing something you do not want. My number would be 2.
Ever flown a 737?
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Old 18th Mar 2019, 18:41
  #1957 (permalink)  
 
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Originally Posted by dufc View Post
Any reason there is not a warning light on the 737 MAX to indicate MCAS has activated?
I can think of one reason: It was meant to be a secret!
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Old 18th Mar 2019, 18:41
  #1958 (permalink)  
 
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Originally Posted by silverstrata View Post


Clearly MCAS is not a runnaway trim condition, otherwise we would be reaching for the cut-out switches every time the speed-trim operated. I think some people here do not realise that the trimmer doing its own thing is operations normal.

And the auro-trim systems are always mis-trimming the aircraft (the trim inputs by the speed-trim system are always wrong, and you always have to re-trim manually). So at what point does ‘operations normal’ become ‘operations abnormal’? At what point do you assume that the trimmer has gone awry..??

Silver
Thx Silver for clearification
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Old 18th Mar 2019, 18:46
  #1959 (permalink)  
 
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The single most powerful control surface on a transport jet is the THS.
Why Boeing would give control of it to a subsystem, like the MCAS is hard to understand.

No amount of hauling (or pushing) on the elevator is going to save you if the THS isn't where it should be.
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Old 18th Mar 2019, 18:48
  #1960 (permalink)  
 
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Does anyone know? If you have a 737 Max , airborne, flaps up, really high speed, full nose down trim, electric stabilizer trimming motors shut off, how much back pressure does it take to raise the nose with the elevator? While applying this large force to the elevator, how much force is required to turn the stabilizer trim hand wheel? How many turns of the hand wheel per degree of stabilizer trim. In other words, is it possible to get into a position in which it is impossible to recover, not enough elevator authority due to force required and or inability to retrim the stabilizer manually due to it binding from a combination of speed and forces being applied through the elevator.
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